[Libreoffice-bugs] [Bug 144699] Use proleptic Gregorian consistently for *all* date formatting and recognition

[bugzilla-daemon at bugs.documentfoundation.org]

https://bugs.documentfoundation.org/show_bug.cgi?id=144699

--- Comment #9 from Mike Kaganski <mikekaganski at hotmail.com> ---
(In reply to Vollbracht from comment #8)
> ISO 6801 defines date conventions AFTER 1582 (and up to 9999) It explicitly
> excludes dates prior to 1583 unless otherwise agreed.

No, it does not exclude these dates - see the EXAMPLE cited from "3.2.1 The
Gregorian calendar". It *only* requires the explicit agreement for using those
- and this agreement is exactly what the standard should establish. And that is
what has been asked on the OASIS mailing list.

> Actually there is an
> agreement among astronomers to use Gregorian type dates prior to 1582 and
> even a year 0 and negative years. But this is no standard in general at all.
> All documents containing date values written in Occident between 1000 and
> 1500 use Julian calendar.

This doesn't mean that we should use them.
Specifically, note that 1582 is *not* the time when "everyone" started to use
Gregorian calendar. So that date has only *very limited* historical meaning
related to "documents containing date values" - most of the world, even those
its parts that use Gregorian today, kept using Julian (and some local
deviations, like switching years at custom months) long after 1582; so when we
use Gregorian for 17th, 18th, 19th centuries, we already break conventions used
for most of the documents of that time.

Hence the use of Gregorian calendar does not aim to follow the historical
facts, but is just a convention for use of uniform, contiguous date system.

Additionally, the reasoning concerning use of "proper calendar for the epoch"
should then go beyond 45 BC - and not use proleptic Julian for those times,
right? Otherwise it would be inconsistent.

But in any case, Gregorian calendar (as described by ODF, and as asked by
*this* issue) should use proleptic Gregorian for all the range covered by dates
representable in LO. Any "proper local calendars" should be used explicitly,
and their introduction should be matter of separate issues.

> Still some conversion functions -
> GREGORIAN(<Julian type date>), JULIAN(<Gregorian type date>) and
> ABURBE(<standard date after 755 B. C.>) might help. They would be great to
> help compare astronomical and historic data. ABURBE() would be very complex
> for date values prior to 709 a.u.c. / 45 B. C. due to 13 months scheme.

These are outside of the scope of this request.

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